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The effect of earthworm (Eudrilus eugeniae) on the bioremediation of used engine oil contaminated soil, amended with poultry manure, was investigated. Investigation into the effect of initial concentration of used engine oil, in soil, for earthworm inoculated samples showed that the biodegradation rate of used engine oil contaminant increased with increasing initial concentration of used engine oil. For initial used engine oil concentration of 5, 10, 15 and 20 g/kg soil, the drop in total petroleum hydrocarbon was found to be -16.91, 20.82, 34.68 and 36.28% respectively after 42 days of treatment. Investigation into the effect of earthworm concentration showed that the use of earthworms did not result in catalysis of the bioremediation process as the extent of biodegradation for the sample without earthworm was found to be higher than those of all concentrations of earthworm considered (5 -20 worms/kg soil). However, the rate of bioremediation was found to increase with increase in earthworm concentration (as earthworm concentration was increased from 5 to 20 worms per kg of used engine oil contaminated soil). Similarly when the rate of bioremediation in the without-earthworm but manually tilled and the without-earthworm and untilled samples where compared with samples inoculated with earthworm for bioremediation, both samples without worms recorded higher bioremediation rates.

Oil pollution is a worldwide prevalent threat to environmental sustainability and the remediation of oil contaminated soils, sediments, surface and underground water is a major challenge for environmental research. Earthworms are an important component of the soil biota and their response to oil pollution needs to be better understood when they are considered for use in bioremediation. Laboratory investigations were undertaken to monitor the survival rate of earthworms (Lumbricus terrestris Lin.) in soils contaminated with used engine oil sourced from three different engines (Motorcycle, Motorcar and Truck engines). The aim was to investigate the effect of used engine oil concentration, in soil, on the survival of earthworms (L. terrestris). The ability of L. terrestris to survive in bioremediated used engine oil contaminated soil was evaluated and it was observed that 100% of earthworms survived in both motorcycle and truck engine used engine oil contaminated soil for concentration as high as 150 g used engine oil/kg soil for a period of 30 days. The highest tolerable concentration of the motorcar used engine oil contaminated soil by the worms was found to be 10 g used engine oil/kg soil.

The distribution of metal in soil from mechanic workshops around Zaria, Nigeria (Latitude: 11° 4' 0 N, Longitude: 7° 42' 0 E) was studied. The types of mechanic workshops considered were motorcycle, motorcar, truck/lorries and generator set. The soils were sampled in August 2010. The results indicated that there was an increase in the metal content of soil in all types of mechanic workshops. The heavy metal (nickel, copper, zinc, lead and arsenic) content of the soil was compared with recommended limits. The percentage composition of some of the heavy metals, in many of the samples, were found to be in excess of the considered set limit, particularly for lead for which the percentage of soil samples analyzed from motorcycle, motorcar, truck/lories and generator set mechanic workshops in excess of the considered recommended set limit was found to be 88.89, 100, 100 and 100% respectively. 11.1% of all the samples analyzed were found to contain arsenic in excess of recommended limit. Statistical analysis of the heavy metal content (one-way analysis of variance) indicated that the Zn and Pb contents of soil from mechanic workshops were not functions of the workshop type (P > 0.05) but the nickel and copper contents were found to be dependent on workshop type (P < 0.05).

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